The pin-outs of the 555 are as follows:

Knowing the three operational modes the 555 timer offers, it's not hard to imagine its many applications in IC circuit designs:

Oscillator: The 555 timer can be used as a simple clock pulse generator (up to 1 or 2 MHz)
Monostable One-Shot: It can be used as a debouncer for switches
Monostable Delay-On: It can be used as a sequential logic control